Contents

Evolution

Ichthyostega and Acanthostega were the first amphibians but however this fish is older than amphibians. Eusthenopteron-Panderichthys-Tiktaalik-Acanthostega-Ichthyostega-Living Reptiles, Amphibians, Birds and Mammals including the non-avian dinosaurs and the non-Devonian amphibians.

Panderichthys and Tiktaalik

Panderichthys and Tiktaalik are Amphibian-like fishes (Tiktaalik has a nose like other Tetrapods). They appear in the Late Devonian Panderichthys appear 380 million years ago and Tikaalik almost lived with the amphibians and lived over 385 million years ago. Tikaalik also could even go to muddy shallows and to the land (A little bit).

The earliest amphibians

Ichthyostega (Means Fish Roof) and Acanthostega (Means Spiny Roof) are the first amphibians from the Latest Devonian first appear in Romer's Gap. The first amphibians came in 374 million years ago.
Romer's Gap amphibians also include Mississippian amphibians like Crassigyrinus before the earliest synapsid appears. Those two amphibians evolve to Other amphibians and even living ones, reptiles including the extinct non-avian dinosaurs and the living ones birds, synapsids including the living ones mammals.

About Eusthenopteron

Eusthenopteron is a genus of prehistoric sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its close relationships to tetrapods. Early depictions of this animal show it emerging onto land, however paleontologists now widely agree that it was a strictly aquatic animal. The genus Eusthenopteron is known from several species that lived during the Late Devonian period, about 385 million years ago. Eusthenopteron was first described by J. F. Whiteaves in 1881, as part of a large collection of fishes from Miguasha, Quebec . Some 2,000 Eusthenopteron specimens have been collected from Miguasha, one of which was the object of intensely detailed study and several papers from the 1940s to the 1990s by paleoichthyologist Erik Jarvik.

Description

Anatomically, Eusthenopteron shares many unique features in common with the earliest known tetrapods. Largest individuals grew up to 1.8 m (6.5 ft) in length. It shares a similar pattern of skull rooting bones with forms such as Ichthyostega and Acanthostega. Eusthenopteron, like other tetrapodomorph fishes, had internal nostrils, (or a choana) which are found only in land animals and sarcopterygians. It also had labyrinthodont teeth, characterized by infolded enamel, which characterizes all of the earliest known tetrapods as well. Like other fish-like sarcopterygians, Eusthenopteron possessed a two-part cranium, which hinged at mid-length along an intracranial joint. Eusthenopteron's notoriety comes from the pattern of its fin endoskeleton, which bears a distinct humerus, ulna, and radius (in the fore-fin) and femur, tibia, and fibula (in the pelvic fin). These appendicular long bones had epiphyseal growth plates that allowed substantial longitudinal growth through endochondral ossification, as in tetrapod long bones. These six appendicular bones also occur in tetrapods and are a synapomorphy of a large clade of sarcopterygians, possibly Tetrapodomorpha (the humerus and femur are present in all sarcoptergyians). Similarly, its elasmoid scales lack superficial odontodes composed of dentine and enamel; this loss appears to be a synapomorphy with more crownward tetrapodomorphs.